America's ambassador to China, Gary Locke, has visited a restive region in Sichuan where ethnic Tibetans have set fire to themselves to protest against rule by Beijing, the US State Department has confirmed.

Locke visited Aba county last month while on a tour of Chongqing and Sichuan aimed at boosting Sino-US trade and met some residents, including ethnic Tibetans, State Department spokeswoman Victoria Nuland said in Washington.

Aba, home to the Kirti Monastery, has seen many self-immolations by monks and other Tibetans, with activists reporting 55 such cases since February 2009.

Beijing does not usually allow foreign dignitaries to visit Tibetan settlements, but Locke went to villages and monasteries to learn more about the lives of Tibetan people and to have the chance to talk to them.

The visit is being seen as a sign that Beijing wants to show it is being more open in dealing with ethnic issues.

A photo posted on Twitter showed Locke shaking hands with a Tibetan monk.

Nuland did not say how long Locke spent in the county and did not reveal his views about the trip, reiterating only that the US had grave concerns about self-immolations among Tibetans.

"We have consistently urged dialogue between the Chinese government and the Tibetan people with regard to those grievances," she said.

Tibetan settlements in China are often off-limits to foreigners. The then executive vice-minister of the Communist Party Central Committee's United Front Work Department, Zhu Weiqun , said last year that China would "never allow foreign forces to interfere in China's internal affairs by any means", when asked whether China would let the European Union send an independent diplomatic team to Tibet.

"I never believe it can settle any problem or bring good to its people for foreign forces to interfere in the internal affairs of another country," he said. "On the contrary, it will intensify the contradiction and even lead to wars."

Analysts said they believed Locke's trip to Aba was made with Beijing's tacit approval, or at least the approval of the foreign ministry, and signified that Beijing wanted to adopt a more flexible approach in dealing with Tibetans.

Beijing may not drastically change its Tibetan policies, but could use the trip as a propaganda tool to subtly deny criticism of them.

"It may be that the Chinese government has the idea that things there are relatively calm at present," said Professor Barry Sautman, a social scientist at Hong Kong University of Science and Technology, who studies Tibetan issues.

"If Locke went there, he would see that things are calm and would say something about his trip that was not entirely negative.

"Perhaps the Chinese government is just thinking that perhaps Locke would come away with some conclusions that are different from Tibetan exile groups'."

Zhao Gancheng , the director of South Asia studies at the Shanghai Institute for International Studies, said: "The Chinese government wants to narrow suspicions towards Beijing, especially in the US."